In a top down roller shade, the entire light blocking material typically wraps around a rotator rail (also referred to as a rotator tube or roller tube) as the shade is raised or retracted. Therefore, the weight of the shade is transferred to the rotator rail as the shade is raised, and the force required to raise the shade is thus progressively lower as the shade (the light blocking element) approaches the fully raised (fully open or retracted) position. Of course, there are also bottom up shades and composite shades which are able to do both, to go top down and/or bottom up. In the case of a bottom/up shade, the weight of the shade is transferred to the rotator rail as the shade is lowered, mimicking the weight operating pattern of a top/down blind.
A wide variety of drive mechanisms are known for extending and retracting coverings—moving the coverings vertically or horizontally or tilting slats. A number of these drive mechanisms may use a spring motor or power assist module to provide the catalyst force (and/or to supplement the operator supplied catalyst force) to move the coverings. For instance, various examples of power assist modules are disclosed in U.S. Pat. No. 9,080,381 (hereinafter the “'381 patent”), entitled “Power Assist Module for Roller Shades,” the disclosure of which is hereby incorporated by reference herein in its entirety for all purposes. In general, the '381 patent discloses power assist modules that can be pre-wound prior to installation and that retain their pre-wound condition even when removed from the associated roller tube or rotator rail.
While the power assist modules of the '381 patent exhibit significant advantages over similar modules and related systems within the marketplace, a need still exists for further refinements and improvements to such power assist modules. For example, due to the configuration and/or material properties of several of the components of the power assist modules, such modules may be subject to wear and/or durability issues, particularly with reference to the mechanical stops utilized within the power assist modules and at the locations of the threaded engagement defined between corresponding threaded components of the power assist modules.
Accordingly, an improved power assist module for a covering for an architectural structure would be welcomed in the technology.